McNie C, Barton D C, Stone M H, Fisher J
School of Mechanical Engineering, University of Leeds.
Proc Inst Mech Eng H. 1998;212(1):49-56. doi: 10.1243/0954411981533818.
Studies of explanted femoral heads have shown that scratches caused by bone cement, bone or metallic particles are present on the rubbing surface. This damage has been cited as a cause of increased wear of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups and it is known that the particulate wear debris produced leads to osteolysis. A series of explanted Charnley femoral heads have been surface characterized using a Talysurf 6 profilometer and found to have scratches with lip heights in the size range 0.1-3.25 microns with an average height of 1 micron giving an average aspect ratio (defined as height/half-width) of 0.1. These geometries were incorporated into a finite element model of a stainless steel asperity sliding over UHMWPE under conditions similar to those in an artificial hip system. It was found that as the aspect ratio of the asperity lip increased, the plastic strains both on and below the surface of the UHMWPE increased non-linearly, but that the magnitude of the strain was independent of the asperity height. The asperity aspect ratio was also found to affect the position of the maximum sub-surface strain, as the asperity aspect ratio was increased the maximum strain rose to the surface. The high plastic strains predicted offer an explanation for the highly elevated wear rates in scratched counterface tests and the aspect ratio of scratch lips is therefore a critical determinant of plastic strain.
对取出的股骨头的研究表明，在摩擦表面存在由骨水泥、骨或金属颗粒造成的划痕。这种损伤被认为是超高分子量聚乙烯（UHMWPE）髋臼杯磨损增加的一个原因，并且已知产生的颗粒磨损碎屑会导致骨溶解。使用Talysurf 6表面轮廓仪对一系列取出的Charnley股骨头进行了表面特征分析，发现划痕的唇高在0.1 - 3.25微米范围内，平均高度为1微米，平均纵横比（定义为高度/半宽度）为0.1。在类似于人工髋关节系统的条件下，将这些几何形状纳入到一个不锈钢微凸体在UHMWPE上滑动的有限元模型中。结果发现，随着微凸体唇的纵横比增加，UHMWPE表面及表面以下的塑性应变呈非线性增加，但应变的大小与微凸体高度无关。还发现微凸体纵横比会影响最大次表面应变的位置，随着微凸体纵横比增加，最大应变上升到表面。预测的高塑性应解释了划痕对偶面试验中磨损率极高的现象，因此划痕唇的纵横比是塑性应变的关键决定因素。
